1. Field of the Invention
The present invention relates to a seven-speed powertrain of an automatic transmission for vehicles.
2. Description of the Related Art
Vehicle companies have been developed and adopted different types of a powertrain of an automatic transmission of vehicles, and most of automatic transmissions generally used in recent day are a four-speed or a five-speed automatic transmission. Recently, a six-speed automatic transmission has been developed and adopted to a vehicle, and a seven-speed automatic transmission is being developed.
As an example, as shown in FIG. 4 (BENZ 7G-TRONIC seven-speed transmission), a powertrain is formed to realize seven speeds by combining two compound planetary gear sets using three clutches, four brakes, and one one-way clutch.
In more detail, a first compound planetary gear set 100 is formed by combining a single pinion planetary gear set and a double pinion planetary gear set, and a planet carrier 102 and a sun gear 104 are shared, so that the first compound planetary gear set 100 has four operational elements of the first sun gear 104, the first planet carrier 102, a first ring gear 106, and a second ring gear 108.
In addition, a second compound planetary gear set 110 is formed by combining two single pinion planetary gear sets, and a third ring gear 112 and a fourth planet carrier 114 are directly connected to each other, so that the second compound planetary gear set 110 has five operational elements of a third sun gear 116, a fourth sun gear 118, a third planet carrier 120, a fourth planet carrier 124, and a fourth ring gear 126.
The first planet carrier 102 is fixedly connected to the fourth ring gear 126 and is connected to a transmission housing 128 via a one-way clutch F.
The first sun gear 104 is variably connected to the first ring gear 106 by a first clutch K1 and is variably fixed to the transmission housing 128 by a first brake B1.
The second ring gear 108 is directly connected to an input shaft 130 so as to always act as an input element, and the third ring gear 112 is variably connected to the input shaft 128 via a second clutch K2.
The third sun gear 116 is variably connected to the fourth sun gear 118 via a third clutch K3, and is variably connected to the transmission housing 128 via a second brake B2.
The first ring gear 106 and the fourth planet carrier 124 are respectively variably connected to the transmission housing 128 via a third brake B3 and a fourth brake B4, and the third planet carrier 120 is fixedly connected to an output shaft 132 so as to always act as an output element.
As shown in FIG. 5, in the above-described seven-speed powertrain, the third clutch K3, the second brake B2, and the third brake B3 are operated at a first forward speed; the third clutch K3, the first brake B1, and the second brake B2 are operated at a second forward speed; the first clutch K1, the third clutch K3, and the second brake B2 are operated at a third forward speed; the first clutch K1, the second clutch K2, and the second brake B2 are operated at a fourth forward speed; the first clutch K1, the second clutch K2, and the third clutch K3 are operated at a fifth forward speed; the second clutch K2, the third clutch K3, and the first brake B1 are operated at a sixth forward speed; and the first clutch K1, the third clutch K3, and the third brake B3 are operated at a seventh forward speed.
In addition, the third clutch K3, the second brake B2, and the fourth brake B4 are operated at a first reverse speed; the first clutch K1, the third clutch K3, and the fourth brake B4 are operated at a second reverse speeds; and the third clutch K3, the third brake B3, and the fourth brake B4 are operated at a third reverse speed.
However, although the above-described seven-speed power train may realize seven forward speeds and three reverse speeds, three frictional elements are operated for each speed, so that a hydraulic pressure control efficiency is deteriorated and a hydraulic pump of a great capacity is needed in order to supply hydraulic pressure to these frictional elements.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.